The long-term objectives of this research proposal are to define the functional roles of Drosophila src-family oncogenes during development. We have concentrated our attention on two members of this gene family: the Drosophila src28C gene and Drosophila epidermal growth factor receptor (DER) gene. Recently completed analysis of the src28C cDNA sequence revealed unique structural aspects of the encoded protein. The protein is more basic than other src-family proteins, with a pI of greater than 10, it has a glycine-rich amino-terminus, and a pattern of conserved amino acids reminiscent of both tyrosine and serine/threonine kinases. Although the capacity of many src- family oncogenes to cause disease when mutated has been well established, the normal physiological roles of these genes have not been revealed. We will study the participation of the src-28C gene in normal development. The DER gene is the only example of a potential mitotic signalling protein in Drosophila. The hypothetical mitotic signalling function of the Drosophila EGF receptor homolog will be tested through the experiments described in this proposal. Therefore the definition of the functional roles of these genes will contribute to knowledge of cellular oncogene function and of Drosophila development. The Specific Aims of this proposal are to: (1) Complete in situ hybridization studies on the expression of src28c and DER RNA during embryogenesis and metamorphosis. (2) Isolate temperature-sensitive mutations in the src28C and DER genes to study their functional roles in cells and tissues where we have documented their expression. (3) Generate site-directed mutations in the src28C and DER genes to study the effect of mutations in specific regions of the proteins. (4) Determine the enzymatic activities of the proteins encoded by the src28C and DER genes.